In the automotive industry the manufacturing of automobiles and parts thereof is done on conveying systems which are usually driven by electric motors. The conveying apparatus is actuated, stopped and reversed automatically and also controlled by operators through the use of function switches. Electromechanic contactors are used as sensors and are secured along the conveying apparatus and are actuated at precise moments either to stop, advance or reverse the operation of electric motors to manipulate the articles being processed. These contactors utilize electromagnets with mechanically actuated contacts which are used to switch the current to these electric motors either to drive the motor clockwise, counterclockwise or just to stop the motor. A function switch is provided for each of these functions. Also the more complex the function performed by the conveyor, for example the automatic stoppage and start of a conveying apparatus in one or two directions, the more complex is the wiring between the function switches, the contacts and the motors, and this requires more and more installation time and highly skilled technicians. Also, it leads to more errors in the wiring due to its complexity and requires large enclosures.
Another disadvantage in this prior art apparatus is that electromagnets are used, and these often produce electric arcs, and accordingly protection must be provided when these electromagnets are utilized in areas where there are gases in the air, such as along the paint sections of such production lines. Also, the use of relays and contactors result in mechanical wear which often require servicing. Still further, when retrofitting an assembly line it becomes very difficult and time consuming to re-wire the control system.